The present invention relates to a device for detecting malfunctions in the operation of the optical unit of a laser printer and transmitting data indicative of detected malfunctions to an external controller.
The optical unit of a laser printer generally includes a semiconductor laser, a collimator lens, a cylindrical lens, a polygonal mirror, an f.theta. lens, a laser drive circuit, an automatic power control (APC) circuit, a polygonal mirror rotator, a horizontal synchronizing signal generator, and an malfunction detection circuit. Since the optical unit and an external controller are connected to each other through a large number of signal lines and various power supply voltages, for example, +5 V, .+-.12 V and +24 V, are applied to the optical unit, it is desired to reduce the number of the signal lines and terminals to simplify the apparatus and decrease the cost thereof. Particularly, because the number of input and output lines of the external controller becomes very large as the number of functions of the laser printer is increased, it becomes increasingly important to reduce the number of input and output lines of the optical unit.
It is of course possible to reduce the number of signal lines by employing a serial signal. However, a separate synchronizing signal and control signal are then additionally required, and a parallel/serial converter and a serial/parallel converter must also be provided, so that the structure of the apparatus becomes more complex and the time required for signal transmission unduly lengthened.